1. Technical Field of the Invention
The present invention relates generally to heaters for use, e. g., in an electrical smoking article and more particularly to a platinum coated heater for use, e.g., in an electrical smoking article.
2. Discussion of the Related Art
Isolated heaters capable of repeatedly converting amounts of energy commonly found in batteries to relatively high temperatures of, e.g., between approximately 700.degree.-1100.degree. C. in approximately one second, are desirable in many situations. For example, high temperature sensors and heat sources are finding numerous applications. Current heaters can comprise a resistive metal heater layer applied to a ceramic substrate. The laminate heater structures often disbond during repeated extreme thermal pulsings of high temperatures and short duration, thereby limiting their applicability in many situations.
For example, previously known conventional smoking devices deliver flavor and aroma to the user as a result of combustion. A mass of combustible material, primarily tobacco, is oxidized as the result of applied heat with typical combustion temperatures in a conventional cigarette being in excess of 800.degree. C. during puffing. Heat is drawn through an adjacent mass of tobacco by drawing or the mouth end. During this heating, inefficient oxidation of the combustible material takes place and yields various distillation and pyrolysis products. As these products are drawn through the body of the smoking device toward the mouth of the user, they cool and condense to form an aerosol or vapor which gives the consumer the flavor and aroma associated with smoking.
Conventional cigarettes have various perceived drawbacks associated with them. Among them is the production of sidestream smoke during smoldering between puffs, which may be objectionable to some non-smokers. Also, once lit, they must be fully consumed or be discarded. Relighting a conventional cigarette is possible but is usually an unattractive prospect for subjective reasons (flavor, taste, odor) to a discerning smoker.
A prior alternative to the more conventional cigarettes are those in which the combustible material itself does not directly provide the flavorants to the aerosol inhaled by the smoker. In these smoking articles, a combustible heating element, typically carbonaceous in nature, is combusted to heat air as it is drawn over the heating element and through a zone which contains heat-activated elements that release a flavored aerosol. While this type of smoking device produces little or no sidestream smoke, it still generates products of combustion, and once lit it is not adapted to be snuffed for future use in the conventional sense.
In both the more conventional and carbon element heated smoking devices described above combustion takes place during their use. This process naturally gives rise to many by-products as the combusted material breaks down and interacts with the surrounding atmosphere.
Commonly assigned U.S. Pat. Nos. 5,093,894; 5,225,498; 5,060,671 and 5,095,921 disclose various heating elements and flavor generating articles which significantly reduce sidestream smoke while permitting the smoker to selectively suspend and reinitiate smoking. However, the cigarette articles disclosed in these patents are not very durable and may degrade, collapse, tear or break from extended or heavy handling. In certain circumstances, these prior cigarette articles may be damaged or damage the cartridge as they are inserted into the electric lighters. Once they are smoked, they are even weaker and may tear or break as they are removed from the lighter.
U.S. patent application Ser. No. 08/118,665, filed Sep. 10, 1993, describes an electrical smoking system including an electrically powered lighter and novel cigarette that is adapted to cooperate with the lighter. The preferred embodiment of the lighter includes a plurality of metallic sinusoidal or serpentine heaters disposed in a configuration that slidingly receives a tobacco rod portion of the cigarette.
These proposed heaters are relatively fragile and are subject to mechanical weakening and possible failure due to stresses induced by inserting and removing the cylindrical tobacco medium and also by adjusting or toying with the inserted cigarette. More significantly, thermal cycling induces thermal stresses and fatigue in the heaters which may result in heater failure. Also, undesirable oxidation of heater material can result from repeated firings.
An electrical smoking article preferably should last between a few months, e.g., six months, to a year or more of normal use defined as equivalent to smoking a pack of more conventional cigarettes per day. Assuming eight puffs per a more conventional cigarette and twenty more conventional cigarettes per pack, the number of thermal pulsings by the heater is significant.
In addition, a heater for a smoking article having a movable tobacco flavor medium such as described in the above-mentioned commonly assigned patent application Ser. No. 08/105,346 requires relatively precise registry, especially if a direct contact between the heater and the tobacco flavor medium is necessary to transfer an adequate amount of heat to the tobacco flavor medium to evolve flavors.
In any heater, e.g., for use in an electrical smoking article, it is desirable to reduce power requirements for a heater to lengthen the useful life between chargings or replacement of the power source.